The present invention relates generally to plastic pipe joints and more particularly to a method of and assembly for making a specifically designed bell end of a bell and spigot pipe joint.
The utilization of a bell end having a locked in gasket is not new. A bell end of this type is illustrated in U.S. Pat. No. 3,924,999 issued to Allen Harris et al on Dec. 9, 1975. The bell end described in this patent is formed by first heating up one end section of a plastic pipe to its range of thermoelastic deformability. Thereafter, the heated end section is moved onto an enlarged core or mandrel and up and over an annular gasket which has been prepositioned around the mandrel, causing the end section to "thin out." Finally, the circumferential sidewalls of the plastic pipe, on either side of the gasket, are deformed inwardly to lock the gasket in place.
The bell end just described is quite satisfactory for its intended use, especially where the overall joint is to be used for nonpressure service, for example sewer service. In this case, the cross-sectional configuration of the bell end does not have to be post thickened or otherwise thickened to compensate for it being enlarged and thinned out compared to the rest of the pipe. However, where the pipe joint is intended for use in pressure service, for example a water pipe, a number of specifications require that the bell end be thicker in cross-sectional configuration than it would be by belling an unthickened pipe. One way to accomplish this is by thickening the end section of the pipe to be belled before belling takes place. This can be carried out during the actual extrusion of the PVC pipe, as described in U.S. Pat. No. 3,264,383, or it can be accomplished after formation of the pipe, as described in co-pending U.S. application Ser. No. 722,187, filed Sept. 17, 1976 now abandoned. In either case, it has been found to be difficult to lock in the gasket in the manner described in the Harris patent (recited above) where the bell end is pre-thickened or post-thickened as just described.
As will be discussed in more detail hereinafter, the present invention is directed to the manufacture of a bell end and particularly one with a locked in gasket. However, in accordance with the present invention, the bell end is formed, its cross-sectional configuration is thickened, and a circumferential sealing gasket is locked in place therein, all at approximately the same time and utilizing one overall assembly, without pre-thickening or post-thickening the pipe.